High Data Rate Wireless Communication Research Articles

Generalized Layered Space–Time Codes for High Data Rate Wireless Communications

We present the architecture of generalized layered space-time codes (GLST) as a combination of Bell Labs layered space-time (BLAST) architecture and space-time coding (STC) in multiple-antenna wireless communication systems. This approach provides both spectral and power efficiency with moderate complexity. The framework is to partition all the available transmit antennas into groups and apply STC on each group as component codes. Based on the mappings from coded symbols to transmit antenna groups, we can construct different GLST systems. Particularly, horizontal mapping and diagonal mapping are introduced and referred to as HGLST and DGLST respectively. The basic decoding of GLST, under quasi-static flat Rayleigh fading environments and assuming perfectly known channel state information (CSI) at the receiver, combines group interference suppression and group interference cancellation techniques. As a result, the individual STC on each group is decoded serially. To improve the overall system performance, we derive the optimal power allocation among all space-time codewords without requiring the knowledge of CSI at the transmitter and suitable for all GLST systems. We also derive the optimal serial decoding order based on the channel realizations at the receiver for HGLST systems without power allocation. Simulation results show that both can provide much improvement. To further enhance the system performance, we propose a low complexity hard-decision iterative decoding method. This method efficiently exploits full receive antenna diversity and, hence, dramatically improves the system performance which is confirmed by simulation.

An Integrated Framework for MC-CDMA Reception in the Presence of Frequency Offsets, Phase Noise, and Fast Fading

The combination of code-division multiple-access and multicarrier (MC) modulation has been proposed to develop high data-rate wireless communication systems. Due to the longer symbol duration in comparison with single-carrier systems, MC systems are more sensitive to various imperfections, including phase noise and frequency offsets due to local oscillators and Doppler spreading due to motion that results in temporal channel variations. The performance of current systems is significantly limited by these imperfections because they disperse the transmitted power in a particular subcarrier into adjacent subcarriers, thereby causing interference between the subcarriers at the receiver. We consider a single-user communication system and use a canonical model for the received signal that efficiently captures the effects of all impairments. The model uses Fourier basis functions that are fixed for all imperfections while the expansion coefficients depend on imperfections. Using the model, we introduce a receiver structure that implements the matched filter (MF), and hence, optimal. The MF is implemented through a Rake receiver in the frequency domain. The receiver fully compensates for frequency offsets as well as phase noise, thereby eliminating the performance loss due to these factors. Furthermore, in contrast to existing designs, it delivers improved performance under fast fading by exploiting Doppler diversity. Finally, the same integrated receiver structure works for all imperfections eliminating the need for devising a separate correction technique for each.

Device Technologies for RF Front-End Circuits in Next-Generation Wireless Communications

Next-generation high data rate wireless communication systems offer completely new ways to access information and services. To provide higher data speed and data bandwidth, RF transceivers in next-generation communications are expected to offer higher RF performance in both transmitting and receiving circuitry to meet quality of service. The semiconductor device technologies chosen will depend greatly on the tradeoffs between manufacturing cost and circuit performance requirements, as well as on variations in system architecture. It is hard to find a single semiconductor device technology that offers a total solution to RF transceiver building blocks in terms of system-on-chip integration. The choices of device technologies for each constituent component are important and complicated issues. We review the general performance requirement of key components for RF transceivers for next-generation wireless communications. State-of-the-art high-speed transistor technologies are presented to assess the capabilities and limitations of each technology in the arena of high data rate wireless communications. The pros and cons of each technology are presented and the feasible semiconductor device technologies for next-generation RF transceivers can be chosen upon the discretion of system integrators.

An Overview of MIMO Communications—A Key to Gigabit Wireless

High data rate wireless communications, nearing 1 Gb/s transmission rates, is of interest in emerging wireless local area networks and home audio/visual networks. Designing very high speed wireless links that offer good quality-of-service and range capability in non-line-of-sight (NLOS) environments constitutes a significant research and engineering challenge. Ignoring fading in NLOS environments, we can, in principle, meet the 1 Gb/s data rate requirement with a single-transmit single-receive antenna wireless system if the product of bandwidth (measured in hertz) and spectral efficiency (measured in bits per second per hertz) is equal to 10/sup 9/. A variety of cost, technology and regulatory constraints make such a brute force solution unattractive, if not impossible. The use of multiple antennas at transmitter and receiver, popularly known as multiple-input multiple-output (MIMO) wireless, is an emerging cost-effective technology that offers substantial leverages in making 1 Gb/s wireless links a reality. The paper provides an overview of MIMO wireless technology covering channel models, performance limits, coding, and transceiver design.

Errata to "space-time codes for high data rate wireless communications: performance criteria in the presence of channel estimation errors, mobility, and multiple paths"

Space-time coding is a bandwidth and power efficient method of communication over fading channels that realizes the benefits of multiple transmit antennas. Specific codes have been constructed using design criteria derived for quasi-static flat Rayleigh or Rician fading, where channel state information is available at the receiver. It is evident that the practicality of space-time codes will be greatly enhanced if the derived design criteria remain valid in the absence of perfect channel state information. It is even more desirable that the design criteria not be unduly sensitive to frequency selectivity and to the Doppler spread. This paper presents a theoretical study of these issues beginning with the effect of channel estimation error. Here it is assumed that a channel estimator extracts fade coefficients at the receiver and for constellations with constant energy, it is proved that in the absence of ideal channel state information the design criteria for space-time codes is still valid. The analysis also demonstrates that standard channel estimation techniques can be used in conjunction with space-time codes provided that the number of transmit antennas is small. We also derive the maximum-likelihood detection metric in the presence of channel estimation errors. Next, the effect of multiple paths on the performance of space-time codes is studied for a slowly changing Rayleigh channel. It is proved that the presence of multiple paths does not decrease the diversity order guaranteed by the design criteria used to construct the space-time codes. Similar results hold for rapid fading channels with or without multiple paths. The conclusion is that the diversity order promised by space-time coding is achieved under a variety of mobility conditions and environmental effects.

Bandwidth- and power-efficient multicarrier multiple access

Orthogonal frequency-division multiple access (OFDMA) gains increasing attention for broadband, high data rate wireless communications. We develop a novel unitary precoded (UP) OFDMA scheme that is particularly appealing for the uplink, because it offers high bandwidth efficiency, and constant modulus transmissions for each user. Theoretical analysis of UP-OFDMA with channel coding shows the performance improvement introduced by unitary precoding. It provides useful guidelines for practical system designs, and also quantifies the performance of UP-OFDMA relative to the single-user bound. Simulations confirm that UP-OFDMA improves performance considerably relative to conventional OFDMA.

Optimal antenna diversity combining for IEEE 802.11a system

IEEE 802.11a/g devices promise to accommodate the increasing consumer demands for high data rate wireless communications. A novel optimal decoding method for receiver antenna diversity combining for a COFDM system is discussed in this paper to provide robust wireless connections for applications such as wireless multimedia communications. The proposed optimal diversity combining integrates the channel equalization, demodulation (bit metrics calculation) and diversity combining in the decoder, which is the maximum likelihood decoding method for the diversity combining for the COFDM system. The proposed method can have about 4-6 dB gain over a single antenna receiver and 2-4 dB gain over a traditional symbol level diversity combining receiver without increasing the implementation complexity.

Space–time coding and signal processing for high data rate wireless communications

Space–time coding and signal processing for high data rate wireless communications

Space-time coding and signal processing for high data rate wireless communications

The information capacity of wireless communication systems can be increased dramatically by employingmultiple transmit and receive antennas [?, ?]. An effective approach to increasing data rate over wireless channels is to employ coding techniques appropriate to multiple transmit antennas, that is space-time coding. Space-time codes introduce temporal and spatial correlation into signals transmitted from different antennas, in order to provide diversity at the receiver, and coding gain over an uncoded system. The spatial-temporal structure of these codes can be exploited to further increase the capacity of wireless systems with a relatively simple receiver structure. This chapter provides an overview of space-time coding techniques and the associated signal processing framework.

Space-time codes for high data rate wireless communication: performance criteria in the presence of channel estimation errors, mobility, and multiple paths

Space-time coding is a bandwidth and power efficient method of communication over fading channels that realizes the benefits of multiple transmit antennas. Specific codes have been constructed using design criteria derived for quasi-static flat Rayleigh or Rician fading, where channel state information is available at the receiver. It is evident that the practicality of space-time codes will be greatly enhanced if the derived design criteria remain valid in the absence of perfect channel state information. It is even more desirable that the design criteria not be unduly sensitive to frequency selectivity and to the Doppler spread. This paper presents a theoretical study of these issues beginning with the effect of channel estimation error. Here it is assumed that a channel estimator extracts fade coefficients at the receiver and for constellations with constant energy, it is proved that in the absence of ideal channel state information the design criteria for space-time codes is still valid. The analysis also demonstrates that standard channel estimation techniques can be used in conjunction with space-time codes provided that the number of transmit antennas is small. We also derive the maximum-likelihood detection metric in the presence of channel estimation errors. Next, the effect of multiple paths on the performance of space-time codes is studied for a slowly changing Rayleigh channel. It is proved that the presence of multiple paths does not decrease the diversity order guaranteed by the design criteria used to construct the space-time codes. Similar results hold for rapid fading channels with or without multiple paths. The conclusion is that the diversity order promised by space-time coding is achieved under a variety of mobility conditions and environmental effects.

Space-time codes for high data rate wireless communication: performance criterion and code construction

We consider the design of channel codes for improving the data rate and/or the reliability of communications over fading channels using multiple transmit antennas. Data is encoded by a channel code and the encoded data is split into n streams that are simultaneously transmitted using n transmit antennas. The received signal at each receive antenna is a linear superposition of the n transmitted signals perturbed by noise. We derive performance criteria for designing such codes under the assumption that the fading is slow and frequency nonselective. Performance is shown to be determined by matrices constructed from pairs of distinct code sequences. The minimum rank among these matrices quantifies the diversity gain, while the minimum determinant of these matrices quantifies the coding gain. The results are then extended to fast fading channels. The design criteria are used to design trellis codes for high data rate wireless communication. The encoding/decoding complexity of these codes is comparable to trellis codes employed in practice over Gaussian channels. The codes constructed here provide the best tradeoff between data rate, diversity advantage, and trellis complexity. Simulation results are provided for 4 and 8 PSK signal sets with data rates of 2 and 3 bits/symbol, demonstrating excellent performance that is within 2-3 dB of the outage capacity for these channels using only 64 state encoders.